Differential pressure control switch



Oct. 3i, 1967 F. D. ATKINSON DIFFERENTIAL PRESSURE CONTROL SWITCH 4 Sheets-Sheet l Filed 0G12. 3, 1966 ifi/V675 B Y W07 Q mmmmsssssmmmmsss@ QQQQQQ@@QQQQQQQQQQQQQQQ mm Nm.

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Oct. 31, 1967 F. D. ATKINSON 3,350,524

DIFFERENTIAL PRESSURE CONTROL SWITCH Filed Oct. 5, 1966 4 Sheets-Sheet 2 E i @-15 /a F. D. ATKINSON DIFFERENTIAL PRESSURE CONTROL SWITCH Oct. 3l, 1967 4 Sheets-Sheet 3 Filedl Oct. '5, 1966 1N VENTO/Q. 95/ffAfM/c/sl* Oct. 31, 1967 F. D. ATKINSON l DIFFERENTIAL PRESSURE CONTROL SWITCH 4 SheetS-Shee 4 Filed Oct. 5, 1966 INVENTOR.

3,350,524 DIFFERENTIAL PRESSURE CONTROL SWITCH Francis D. Atkinson, Redlands, Calif., assignor to the United States of America as represented by the Secretary of the Air Force Filed Oct. 3, 1966, Ser. No. 584,019 7 Claims. (Cl. 20o-82) The invention described herein may be manufactured and used by or for the United States Government for governmental purposes without payment to me of yany royalty thereon.

This invention relates to a differential pressure Control switch for use in high pressure systems.

One object of the invention is to provide a differential pressure control switch which will operate at a low differential pressure.

Another object of the invention is to provide a differential pressure control switch that will withstand high differential pressures.

A further object of the invention is to provide a differential pressure control switch that provides make-andbreak adjustment and differential pressure operating adjustment.

These and other objects will be more fully understood from the following detailed description taken with the drawing, wherein:

FIG. 1A is a block diagram of a high pressure gas system in which the device of the invention might be used;

FIG. 1B is a front elevational view of the differential pressure control switch of the invention;

FIG. 2 is a right end view of the differential pressure control switch of FIG. 1B;

FIG. 3A is an enlarged sectional view of the piston housing assembly of the device of FIG. 1 taken along the line 3 3 in FIG. 2;

FIG. 3B is an enlarged sectional view of the switch housing assembly of the device of FIG. 1 taken along the line 3 3 in FIG. 2;

FIG. 4 is an enlarged sectional view of the switch housing assembly of the device of FIG. 1 taken along the line 4 4 in FIG. 2;

FIG. 5 is a front elevational view of the piston rod guide assembly for the device of FIG. 3A;

FIG. 6 is a sectional view of the piston rod guide assembly of FIG. 5 taken along the line 6 6;

FIG. 7 is the top view of the switch contact element for the device of FIG. 3B;

FIG. 8 is an end view of the device of FIG. 7;

FIG. 9 is an end vie'w of the outer switch housing for the device of FIG. 3B; and

FIG. 10 is a sectional view of the device of FIG. 9 along the line 10 10.

The switch of the subject invention is for use in a system shown in FIG. 1A. A high pressure gas such as gaseous nitrogen at' about 6000 p.s.i. is stored in a high-pressure storage tank 11. An automatic air-open, spring-close valve 12 is connected between the storage tank 11 and the loads shown at 13, 14-and 15. The operation of valve 12 is remotely controlled by air from an air supply 16. Manual control of the valve, in case of failure downstream of the valve, would not be fast enough to prevent damage to equipment and danger to life. Therefore, some automatic means is required to close valve 12 in case such failure should occur. A ldifferential pressure control switch 18, which is connected in shunt across valve 12, operates an air control valve 19 in the air supply line to valve 12. Since the full pressure cannot be applied suddenly to the load without causing great damage, the switch 18 must be such that the valve 12 will not be turned on until the differential pressure is reduced to a predetermined desired level. A

l United States Patent Office 3,350,524 Patented Oct. 31, 1967 bypass valve 20 is provided to gradually bring the load pressure up to the desired value.

The pressure control switch must operate to close the valve at a predetermined differential pressure and must be able to withstand the full 6000 p.s.i. differential pressure when the valve 12 is closed. The switch of this invention is provided to operate at a differential pressure of approximately 14 p.s.i. with an adjustment to permit operation at anywhere from 6 p.s.i. to 100 p.s.i. differential pressure. The differential pressure acts to move a piston against a first adjustable spring. For high differential pressures a stop is provided for the piston. A second spring is provided to slow the piston as it approaches the stop and to to move the piston off of the top when the differential pressure is reduced to a predetermined value so that the pressure on the low pressure side of the switch can act over the whole surface of the piston. A spring operated switch is controlled by the movement of the piston to close the air control valve to shut off the air supply to the valve 12. The positioning of the switch is made adjustable so that the opening time of the switch can be controlled.

As shown in FIG. 1B the differential pressure switch assembly 18 has a piston asembly 21 and a switch assembly 22. The piston assembly 21 and the switch assembly 22 are secured to each other by means of a plurality of bolts 23 and nuts 24 to provide a sealed chamber. The differential pressure switch assembly has a high-pressure input 25 and a low-pressure input 26.

The piston assembly 11, as shown in FIG. 3A, has a piston housing 28 with a piston 29 within a cylindrical chamber. A seal groove 27 is provided for sealing assembly 21 to assembly 22. The piston 29 is connected to a piston rod 30 by means of a threaded shaft 31, spring retainer 32 and a nut 33. An O-ring seal 34 is provided between piston 29 and the spring retainer 32. A pair of O-rings 36 are provided between the piston 29 and the chamber wall 37.

The piston rod 30 fits into a piston rod guide 38 as shown in FIG. 6. A first spring 39 surrounds the piston rod 30 and piston rod guide 38. A spring guide 40 surrounds the spring 39 and is threaded into housing 28. A second spring 41 surrounds the spring guide 40 and abuts flange 42.on spring guide 40. A tension adjustment for spring 39 is provided at 43 which is provided with a lock nut 44. A cap 45 with -an O-ring 46 covers the adjustment device 43.

The switch housing 22 has an inner stationary switch housing 48 and a movable switch support 49. The stationary switch housing 48 has two end members 50 and 51 which are interconnected by a pair of plate members 52. The movable switch support 49 has a rectangular cross section and fits rectangular opening 55 in the end member 50 and rectangular recess 56 in end member 51. A stationary contact 57 shown in greater detail in FIGS. 7 and 8 has a contact member 58 and a lead connecting member 59. The contact member 5S is inserted into .a hole 60 in movable support 49 and the lead connecting member 59 fits into a slot 62 in the side of support 49. A movable switch block 64 is secured to a leaf spring 65 by means of a bolt 66. The other end of the leaf spring is inserted and held by a friction fit in slot 67 or pivot arm 68. The pivot arm 68 pivots on pin 69 and is controlled by shaft 31. A spring 71 on spring guide pin 72 moves the switch block 64 away from the stationary contact 58 when shaft 31 moves away from the pivot arm 68. The spring guide pin 72 is secured to the pivot arm `68 by a pin 74 and passes through pin guide 75 which is secured to movable support 49. Adjustment of the position of the movable support is made by means of a threaded adjustment shaft 78. The shaft 78 passes through a longitudinal hole 79 in movable support 49. A washer 80 engages a groove 81 in support 49 and lis held in place by a nut 82. A threaded plug 84 with an O-ring seal 85 seals adjustment chamber 86 from the atmosphere.

Bayonet leads 88 and 89 fit into female contacts 90 and 91, respectively. Flexible leads 92 and 93 connect contacts 90 and 91 to switch block 64 and connecting member 59, respectively. Insulation members 96, 97 and 98 surround the bayonet leads 88 and 89. Threaded retaining plugs 99 secure the insulating members 96, 97 and 98 and the bayonet leads in place.

The high-pressure gas connected at input 25 passes through central opening in insulator 100, then through radial channels 101 in end member 50, then through holes 102 in end member 50 and holes 103 ,in end member 51 to reach the high-pressure end of piston 29. A groove 104 is provided to match with groove Z7 for receiving the seal 105.

In the operation of the device under normal operating conditions, there is .a pressure differential of approximately 3 p.s.i. across valve 12. If some failure occurs, such as a break in a line downstream, the sudden drop in pressure across valve 12 will cause the pressure at the input 26 to drop below the pressure at input 2S. If the differential pressure exceeds a predetermined value as determined by the adjustment of the device 43, for example 14 p.s.i., the piston 29 will move toward stop 35 on spring guide 40. When the piston has moved an amount as determined by the position of movable support 49, the shaft 31 permits the pivot arm, under the action of spring 71, to move leaf spring 65 and switch block 64 so as to break contact with switch contact 58, thus closing valve 19 and shutting off air flow to the valve 12.

If the differential pressure across piston 29 is great enough the spring 41 absorbs the shock and eases the spring retainer 32 against stop 35 so that the switch assembly will withstand the high differential pressure.

After repair of the break, bypass valve 20 is manually operated to permit the pressure downstream to come up to the desired level. When the differential pressure returns to about 500 p.s.i. the spring 41 moves the piston 29 off of the stop so that the downstream pressure can act over the whole area of the piston to balance the pressure on the piston when the differential pressure again returns to the desired value. The shaft 31 will then move the pivot arm 68 to close the switch contacts which will then permit air to flow to valve 12 to open this valve. When valve 12 opens, bypass valve 20 is closed.

While the spring 41 is shown as much larger than spring 39, it is to be understood that other arrangements could be used and the particular springs used would be determined by the particular lapplication for the device.

There is thus provided a differential pressure control switch which will operate at low differential pressures and which will withstand high differential pressures.

While a certain specific embodiment has been described, it is to be understood that numerous changes may be made without departing from the general principles and scope of the invention.

I claim:

1. A differential pressure control switch comprising: a sealed housing having a cylindrical chamber therein; a piston within said chamber; switch means within said chamber on one side of said piston; said switch means having a stationary contact and a movable contact; means for urging said movable contact to its open position;

means attached to said piston for holding said movable contact against said stationary contact; means for -admitting a gas under pressure to the switch side of said piston; means for admitting `a gas under pressure to the other side of said piston; spring means, on the side of said piston remote from said switch means, for urging said piston toward said switch to maintain said switch in its closed position until the differential pressure across said piston reaches a predetermined value; an annular stop means adjacent said spring means for stopping the movement of said piston for high differential pressures across said piston; means adjacent said stop means for easing said piston into contact with said stop; a pair of output leads for said switch sealed into the wall of said housing and means for connecting said switch contacts to said output leads.

2. The device as recited in claim 1 having means for adjusting the tension of said spring means to thereby adjust the differential pressure required for opening the switch means.

3. The device as recited in claim 2 having means for adjusting the opening and closing time of said switch means.

4. A differential pressure control switch comprising; a first chamber; a switch having a movable contact and a stationary contact; means for movably supporting said switch within said rst chamber; means, supported by said movable support means, for urging said movable contact away from said stationary contact; a second chamber sealed to said rst chamber; a piston within said second chamber; means for admitting gas under pressure to said first chamber on one side of said piston; means fior admitting gas under pressure to said second chamber on the other side of said piston; means connected to said piston for maintaining said switch in its closed position when the differential pressure across said piston is below a predetermined value; a irst spring in said second chamber on the side 'of said piston remote from said switch for urging said piston tow-ard said switch unless the differential pressure across said piston reaches a predetermined value; a cylindrical spring guide providing a piston stop means surrounding said first spring; a second spring, surrounding said spring guide, for easing said piston toward said stop means, for large differential pressures across said piston and aipair of connector leads connected to the contacts of said switch.

5. The device as recited in claim 4 having means for adjusting the tension of said first spring to thereby adjust the differential pressure `for the operation of said switch.

6. The device as recited in claim 4 having means for adjusting the position of said movable switch support to -thereby select the opening and closing time for said switch.

7. The device as recited in claim 5 having means for adjusting the tension of said rst spring to thereby adjust the differential pressure for the operation of said switch.

References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, Primary Examiner. H. BROOME, Assistant Examiner, 

1. A DIFFERENTIAL PRESSURE CONTROL SWITCH COMPRISING: A SEALED HOUSING HAVING A CYLINDRICAL CHAMBER THEREIN; A PISTON WITHIN SAID CHAMBER; SWITCH MEANS WITHIN SAID CHAMBER ON ONE SIDE OF SAID PISTON; SAID SWITCH MEANS HAVING A STATIONARY CONTACT AND A MOVABLE CONTACT; MEANS FOR URGING SAID MOVABLE CONTACT TO ITS OPEN POSITION; MEANS ATTACHED TO SAID PISTON FOR HOLDING SAID MOVABLE CONTACT AGAINST SAID STATIONARY CONTACT; MEANS FOR ADMITTING A GAS UNDER PRESSURE TO THE SWITCH SIDE OF SAID PISTON; MEANS FOR ADMITTING A GAS UNDER PRESSURE TO THE OTHER SIDE OF SAID PISTON; SPRING MEANS, ON THE SIDE OF SAID PISTON REMOTE FROM SAID SWITCH MEANS, FOR URGING SAID PISTON TOWARD SAID SWITCH TO MAINTAIN SAID SWITCH IN ITS CLOSED POSITION UNTIL THE DIFFERENTIAL PRESSURE ACROSS SAID PISTON REACHES A PREDETERMINED VALUE; AN ANNULAR STOP MEANS ADJACENT SAID SPRING MEANS FOR STOPPING THE MOVEMENT OF SAID PISTON FOR HIGH DIFFERENTIAL PRESSURES ACROSS SAID PISTON; MEANS ADJACENT SAID STOP MEANS FOR EASING SAID PISTON INTO CONTACT WITH SAID STOP; A PAIR OF OUTPUT LEADS FOR SAID SWITCH SEALED INTO THE WALL OF SAID HOUSING AND MEANS FOR CONNECTING SAID SWITCH CONTACTS TO SAID OUTPUT LEADS. 